The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Is Mounjaro 15mg Equivalent to Wegovy?
Mounjaro 15mg and Wegovy are two different weight loss injections, and there is no exact dose-for-dose equivalence between them. However, Mounjaro 15mg (the maximum dose) is approximately equivalent to Wegovy 2.4mg (also the maximum dose) in terms of weight loss potential, though they work through different mechanisms. Both are prescription-only medicines licensed in the UK, and which one suits you best depends on individual health factors assessed by your prescriber. Our GLP-1 weight loss calculator can help you explore potential outcomes with different medications.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro and Wegovy Compare: Clinical Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that activates two hormone pathways, whereas Wegovy (semaglutide) is a GLP-1 receptor agonist only. This difference in mechanism means they cannot be directly converted dose-for-dose.
Based on clinical trial data, the approximate dose equivalence is:
- Mounjaro 5mg ≈ Wegovy 0.5mg
- Mounjaro 10mg ≈ Wegovy 1.7mg
- Mounjaro 15mg ≈ Wegovy 2.4mg
In the SURMOUNT-1 trial, Mounjaro 15mg achieved average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy 2.4mg achieved approximately clinically studied weight loss over 68 weeks. Individual results vary significantly, and both medications must be used alongside reduced-calorie diet and increased physical activity.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Which Medication is Right for You?
Neither Mounjaro nor Wegovy is universally "better" — suitability depends entirely on individual health factors, medical history, and prescriber assessment. Both are prescription-only and require a clinical evaluation before being prescribed. Your GP or a licensed prescriber will assess your eligibility (typically BMI 30 or above, or 27 with weight-related health conditions) and consider any contraindications, other medications, and personal preferences.
Some people respond better to dual-mechanism medications like Mounjaro, whilst others have equal success with Wegovy's single GLP-1 mechanism. If you're interested in either option, a prescriber can discuss both, explain how the tirzepatide KwikPen delivery works versus semaglutide pens, and help you make an informed decision. Use our free BMI calculator to check your starting point before any consultation.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Mounjaro 15mg stronger than Wegovy 2.4mg?
They are not directly comparable because Mounjaro is a dual GIP+GLP-1 agonist whilst Wegovy is a single GLP-1 agonist. Clinical trial data suggests Mounjaro 15mg may produce slightly higher average weight loss (20.9% vs 14.9%), but individual results vary significantly. Suitability is a personal decision made with your prescriber.
Can I switch from Wegovy to Mounjaro?
Yes, some people do switch between these medications under prescriber guidance. However, there is no official NHS-approved conversion chart. Any switch must be managed by your prescriber, who will assess whether it's appropriate and oversee the transition safely. Do not change medications without medical advice.
How long does it take to reach the maximum dose?
Mounjaro takes approximately 20 weeks to reach 15mg (4 weeks per dose level, starting at 2.5mg). Wegovy takes approximately 16 weeks to reach 2.4mg. Both require a step-by-step dose titration to monitor tolerability and minimize side effects.
Are both medications available on the NHS in the UK?
Both Mounjaro and Wegovy are MHRA-approved and NICE-recommended for NHS specialist weight management services in certain areas. However, NHS availability varies significantly by region, and waiting lists can be lengthy. Both are also available through private online prescribing services following an online clinical assessment with a UK-licensed prescriber.
What are the main side effects of both medications?
Common side effects include nausea, diarrhoea, constipation, and stomach pain, especially during dose escalation. Most side effects tend to improve over time. Serious side effects are rare but can include pancreatitis and gallbladder issues. Always report any severe or persistent symptoms to your prescriber immediately.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.